New Radio (NR) access technique is currently discussed in 3GPP (3rd Generation Partnership Project). The NR concept includes new waveform, new multiple access schemes, symbol and subcarrier numerologies, and new frame structures. Compared to legacy communication systems such as Wideband Code Division Multiple Access (WCDMA) and Long Term Evolution (LTE), NR is targeted to include many unique characteristics such as flexible and scalable operations and smaller sub-frame/frame duration (e.g., in the order of 100-200 microseconds (μs)) to support low latency communications.
Multiple-input and multiple-output (MIMO) is the use of multiple antennas at both a transmitter (e.g., a base station “BS” and/or user equipment “UE”, otherwise referred to as a mobile device) and a receiver (e.g., a BS and/or UE) in order to improve link and or system capacity between the transmitter and the receivers. Massive MIMO, otherwise referred to as a MaMi network, refers to using a large number of antennas (e.g., equal to or greater than a threshold number) at the transmitter, receiver or both. For example a base station may have hundreds of antennas, arranged in an antenna array, while the user equipment will have at least one and, optionally, two to four antennas.
Typically, for TDD system the information stream between a base station (BS) and a user equipment (UE) is operated with a time division duplex and is split into timeslots or sections embedded in a frame structure, commonly referred to as a radio frame. Different timeslots for uplink (UL) data communications and downlink (DL) data communications are provided for communicating information from the UE to the BS (uplink) and for communicating information from the BS to the UE (downlink). Also other duplex methods can be considered, where uplink and downlink communication besides time can be separated by other means, e.g. frequency and/or coding. As part of the radio frame, the information communicated between the UE and the BS includes, in addition to payload information, pilot signals that are used in the estimation of the communication channel. Due to limited coherence time in some systems the validity of this pilot signal is limited. Therefore the pilot signal can be positioned in the beginning of the radio frame, to enable usage of the pilot information during following parts of the same radio frame. In order to calibrate the antennas in a MaMi network and focus energy to the UEs from the antennas, thereby maximizing antenna gain, the UEs transmit a pilot signal, in a dedicated time slot within a radio frame, which is listened for by all the antennas at the BS. The validity of the pilot signal that is transmitted from the UE is very time limited (i.e., time coherency is minimal). If the UE is physically moved a short distance the pilot signal will no longer be valid and the channel will appear different. Therefore, the pilot signal needs to be transmitted on the uplink frequently (e.g., once every millisecond (ms) or the like).
FIG. 1 illustrates a frame structure to support low latency (i.e., minimal delay), in accordance with the prior art. In NR, a frame structure that supports the low latency DL traffic requires DL resources followed by the UL resources such that the UL resources contain acknowledgement (ACK)/negative-acknowledgement (NACK) information, which is sent immediately after the DL transmission, as shown in FIG. 1.
FIG. 2 illustrates a frame structure to support massive MIMO, in accordance with the prior art. In MaMi network, the UL transmission is allocated first and followed by the DL transmission. This is done to enable the BS in the MaMi network to process the UL pilot and determine antenna configuration parameters, as shown in FIG. 2. Based on the received pilot signal, a BS may configure the transceivers of its antenna array according to spatial and environmental conditions for subsequent transmission of payload information. The UL pilots for each UE in a MaMi network are orthogonal to each other and serve as reference for both the BS antenna array configuration and calibration of the constellation diagram. In this regard, each individual UE is allocated to a unique time/frequency resource for the pilot transmission. Typically, the UL pilot is used to calibrate the constellation diagram for the BS to be able to decode the UL payload. While the calibration of the constellation diagram is ideally not required at the UE side, it is unavoidable due to channel erosion, reciprocity errors, interference, or the like. For the DL, the UL pilot is again used to determine pre-coding for the DL payload. This DL payload does not need to be on an orthogonal time/frequency resource as it is pre-coded for spatial diversity.
For asymmetric traffic typically dominated by DL transmission, a UL pilot is scheduled with a repetition rate corresponding to at least the coherence time to update the BS with the channel response. Since the BS requires a specific amount of time to determine a precoding matrix, the UL pilot signals may be interleaved. In this regard, the BS uses the received UL pilot signal from a first frame to determine antenna configuration parameter for transmission of payload in the second frame (a frame that follows the first frame directly). At higher frequencies fixed beams may be used for the DL to transmit frames with a DL pilot for the UE to configure its antennas. The UL pilots are used for calibration of constellation points and also beam steering or beam selection at the BS. In this regard, the UL pilots may be spatially integrated with the UL payload.
In a two-way communication system over wireless channels, both DL and UL pilots are typically repeatedly required to be transmitted between the BS and UE to estimate channel properties, such as link adaptations, synchronization, power control, or the like.
To realize the capabilities of 5G (5th Generation) wireless access, such as low latency communication, very high data rates, ultrahigh reliability, energy efficiency, and extreme device densities, the present invention proposes methods of adopting the frame structure of massive MIMO technology in the 5G NR technology. The techniques proposed herein can also be applied to wireless LAN standardization that they require the operation of massive number of antennas (e.g., 802.11ay) operating in time division duplexing (TDD) mode.